1. Technical Field
The present invention relates to an intermediate transferer equipped in image forming apparatuses such as copiers and printers, particularly to an intermediate transferer preferably used in full-color image formation and to an image forming apparatus using the same.
2. Description of the Related Art
In the conventional art, a belt, especially a seamless belt, has been used for various purpose, as a member in an electrophotographic image forming apparatus. In recent years, an intermediate transfer belt system has been used in a full color image forming apparatus, where the intermediate transfer belt system includes superimposing developed images of four colors, yellow, magenta, cyan, and black temporarily on an intermediate transfer member, and collectively transferring the superimposed images onto a transfer medium, such as paper.
As for the aforementioned intermediate transfer belt, a system using developing units of four respective colors to one photoconductor has been used, but this system has a problem that a printing speed thereof is slow. Accordingly, to achieve high speed printing, a quarto-tandem system has been used, where the tandem system includes providing photoconductors of four respective colors, and an image of each color is continuously transferred to paper. In this system, however, it is very difficult to accurately position images of colors to be superimposed, as the paper is affected by the fluctuations of the environment, which causing color shift in the image. Accordingly, currently, an intermediate transfer belt system has been mainly adapted for the quarto-tandem system.
Under the circumstances as mentioned above, the higher requirements for properties (high speed transferring, and accuracy for positioning) of a intermediate transfer belt have been demanded than before, and therefore it is necessary for an intermediate transfer belt to satisfy these requirements. Especially for the accuracy for positioning, it has been required to inhibit variations caused by deformation of an intermediate transfer belt itself, such as stretching, after continuous use thereof. Moreover, an intermediate transfer belt is desired to have flame resistance as it is provided over a wide region of a device, and high voltage is applied thereto for transferring. To satisfy these demands, a polyimide resin or a polyamideimide resin that is a highly elastic and highly heat resistant resin, has been mainly used as a material of an intermediate transfer belt.
However, since an intermediate transfer belt formed of a polyimide resin has high strength and high surface hardness, it applies high pressure to a toner layer when transferring a toner image, resulting in occasional void images because a toner unevenly aggregates and a part of an image is not transferred. In addition, the intermediate transfer belt has low followability with a contact member such as a photoconductor and a paper, resulting in occasional uneven transfer because of partial defective contact (gap).
Recently, full-color electrophotographic images have been more frequently formed on various papers such as slippery coated papers having high smoothness, and recycle papers, emboss papers, Japanese papers and craft papers having rough surfaceness. The followability on papers having different surfaceness has importance, and poor followability causes uneven image density or color tone.
In order to solve this problem, various intermediate transfer belts each formed of a substrate and an elastic layer comparatively having flexibility layered thereon are disclosed. However, a surface layer having flexibility decreases in transfer pressure and releasability although improving in followability to paper convexities and concavities. Therefore, a toner does not release well therefrom, resulting in lowering of transfer efficiency. Further, it has lower abrasion resistance and scratch resistance.
In order to solve this problem, a method of forming a protection layer is disclosed. However, when a material having fully high transferability is coated on the flexible layer, it is unable to follow flexibility thereof, resulting in crack or peeling.
Japanese Patent No. JP-4810673-B2 (Japanese published unexamined application No. JP-2007-212921-A) discloses a double-layered intermediate transferer including a substrate and a surface layer overlying the substrate, in which the outermost surface has higher hardness to improve transferability. However, this still has poor followability to recycle papers, emboss papers, Japanese papers and craft papers having rough surfaceness and low transferability.
Japanese Patent No. JP-4973781-B2 (WO2009/145173) discloses a double-layered intermediate transferer including a substrate, an elastic layer overlying the substrate, a surface layer overlying the elastic layer, in which the surface layer is a thin film hard coating to improve durability and transferability. However, this still has hard outermost surface and low followability to papers having rough surfaceness.
Japanese published unexamined application No. JP-2012-181244-A discloses polyrotaxane used in a surface layer of a photoconductor improves durability thereof. However, this relates to a photoconductor, and differs from the present invention. Japanese Patents Nos. JP-4376846-B2, JP-4376848-B2, JP-4376849-B2 and JP-4385165-B2 (Japanese published unexamined applications Nos. JP-2007-099973-A, JP-2007-099989-A, JP-2007-099993-A and JP-2007-099977-A, respectively) relate to automotive paints.
Japanese Patent No. JP-5071564-B2 (Japanese published unexamined application No. JP-2012-158724-A) discloses a surface layer formed of a material in which polyurethane which is a polymer of an acrylic resin and isocyanate, and polyimide are mixed to improve damage reparability and transferability. However, compatibility between polyurethane and polyimide is low, which causes uneven hardness. In addition, images are likely to have spot uneven image density. Further, followability to transfer media and toner releasability are not improved, and uneven transfer is not solved yet. Further, an untransferred toner is not removed by a cleaning blade from a layer having flexibility.